The present invention pertains to a filter arrangement, which is arranged above and on a process container, in which particulate product is treated, e.g., by mixing, drying, granulation, pelletizing and/or coating the product. The process may consist of agglomerating or granulating product particles having the fineness of dust in the process container into larger particles or of providing particulate starting product with a coat by means of coating. A bottom, which is permeable to air and has passages, especially in the form of slots, is usually provided for this in the lower region of the process container.
A filter unit, comprising a cylindrical exterior filter and an interior filter tapering conically from bottom to top, is known from DE 40 29 994 C2.
Air contaminated with particles, such as dusty air, is delivered in the product-treating process operation from the outside through the exterior filter and from the inside through the interior filter into an intermediate space between the exterior filter and the interior filter of the filter unit and via an opened valve to a gas outlet.
To blow off dust collected on the outside of the exterior filter and on the inside of the interior filter, the valve is closed and an air path from a gas inlet for clean gas to the intermediate space between the interior filter and the exterior filter is opened via another valve, so that blowing off of particles adhering to the outside of the exterior filter and to the inside of the interior filter can take place in counterflow. Complete cleaning is not always possible hereby on the side of the filters facing the dusty air, and removal of filter dust having penetrated into the clean air region can be performed with difficulty only. For complete cleaning, the filter unit must be removed and disassembled and the individual filters must then be cleaned one by one. Consequently, cleaning in place (CIP) is not possible in the state of the art without removal of the filter cartridges.